A common method for affixing items to solid walls is to drill a hole of measured depth and diameter in the wall and to insert an expansion anchor into the hole, expanding the anchor to thereby hold a supported item. A common form of inexpensive expansion anchor is the plastic plug anchor (generally of a relatively hard plastic such as nylon or pvc) of suitable snug fitting size which is inserted into the drilled hole. A screw is screwed into the open end of the plug to cause the plastic of the anchor to expand against the walls of the hole (less desirable is a plug anchor in which a nail is hammered into the plug). The item to be supported by the wall is held by the screw and kept in place by the anchor. Holding is effected by an increase of frictional engagement between the plastic plug and the walls of the hole caused by the screw. The plug anchor is provided with a central hollow for accommodation of the screw without lockup during installation.
In a more recently developed plug anchor, as disclosed in U.S. Pat. No. 4,752,170, an extrudible material such as polypropylene is used in place of the more common nylon or pvc and the anchor is configured to have nesting arms which, when nested, form a completely or substantially completely solid anchor body for a significant portion of the length of the anchor. In U.S. Pat. No. 5,161,296, a method of using the aforementioned nested anchor is described wherein the essentially solid nature of the anchor is utilized to effect, with screws or bolts of dimension matched to the anchor, extraordinary tensile holding strength. The disclosures of both of the above patents are incorporated herein by reference thereto.